1. Field of the Invention
The present invention provides an improved method for the production of propylene from a C.sub.4 or higher hydrocarbon feed. Specifically, in accordance with the invention, a higher hydrocarbon is converted over a zeolite catalyst at conditions which favor production of a product mixture containing ethylene and propylene. Propylene is separated from this product mixture and recovered. The ethylene from the reaction mixture is metathesized with C.sub.4.sup.+ olefin in order to form further quantities of product propylene.
2. Description of the Prior Art
Propylene is an important chemical of commerce. In general, propylene is largely derived from selected petroleum feed materials by procedures such as steam cracking which also produce high quantities of other materials. At times, there exist shortages of propylene which result in uncertainties in feed supplies, rapidly escalating raw material costs and similar situations which are undesirable from a commercial standpoint. Also, due to imbalances in hydrocarbon values, economics favor using alternate feedstocks provided an effective process for forming propylene was available.
Methods are known for the conversion of higher hydrocarbons to reaction mixtures comprised of the C.sub.2 and C.sub.3 lighter olefins. For example, published European patent applications Publication Nos. 0109059 and 0109060 provide illustrative teachings of conditions and catalysts which are effective for the conversion of higher hydrocarbons such as butenes to the lighter olefins. Copending application Ser. No. 07/343097, filed Apr. 25, 1989, likewise provides a comprehensive teaching of prior methods for the production of the lower olefins from higher hydrocarbon feed materials. In certain instances, it would be distinctly advantageous to provide means for still further improving yields of propylene which result from the conversion of less expensive higher hydrocarbon feed materials.
The disproportionation or metathesis of olefins is likewise a known reaction. In this regard, reference can be made to Banks U.S. Pat. No. 3,261,879, to Banks "Olefin Metathesis Technology and Application," Applied Industrial Catalysis, Volume III, Chapter 7, Pages 215, et seq., Leach, Editor (1984). In addition, olefin metathesis reaction and catalysts useful therefor are described in U.S. Pat. Nos. 3,883,606, 3,915,897, 3,952,070, 4,180,524, 4,431,855, 4,499,328, 4,504,694, 4,517,401 and 4,547,617.
Despite developments in the art, it remains desirable to provide methods for producing higher yields of propylene from the less expensive higher hydrocarbon feed materials.